Iowa State physicist Jigang Wang, right, examines graphene monolayers grown on a substrate mounted in a cooper adapter as graduate students Tianq Li, far left, and Liang Luo look on in Wang's laboratory. Credit: Steve Jones/College of Liberal Arts and Science, Iowa State University

Graphene has caused a lot of excitement among scientists since the extremely strong and thin carbon material was discovered in 2004. Just one atom thick, the honeycomb-shaped material has several remarkable properties combining mechanical toughness with superior electrical and thermal conductivity.

Now a group of scientists at Iowa State University, led by physicist Jigang Wang, has shown that graphene has two other properties that could have applications in high-speed telecommunications devices and laser technology  population inversion of electrons and broadband optical gain.

Wang is an assistant professor in the Department of Physics and Astronomy in the College of Liberal Arts and Sciences at Iowa State University. He also is an associate scientist with the Department of Energy's Ames Laboratory.

Wang's team flashed extremely short laser pulses on graphene. The researchers immediately discovered a new photo-excited graphene state characterized by a broadband population inversion of electrons. Under normal conditions, most electrons would occupy low-energy states and just a few would populate higher-energy states. In population-inverted states, this situation is reversed: more electrons populate higher, rather than lower, energy states. Such population inversions are very rare in nature and can have highly unusual properties. In graphene, the new state produces an optical gain from the infrared to the visible.

Simply stated, optical gain means more visible light comes out than goes in. This can only happen when the gain medium is externally pumped and then stimulated with light (stimulated emission). Wang's discovery could open doors for efficient amplifiers in the telecommunication industry and extremely fast opto-electronics devices.

Graphene as a gain medium for light amplification

"It's very exciting," Wang said. "It opens the possibility of using graphene as a gain medium for light amplification. It could be used in making broadband optical amplifiers or high-speed modulators for telecommunications. It even provides implications for development of graphene-based lasers."

Wang's team unveiled its findings in the journal Physical Review Letters on April 16. In addition to Wang, the paper's other authors are Tianq Li, Liang Luo and Junhua Zhang, Iowa State physics graduate students; Miron Hupalo, Ames Laboratory scientist; and Michael Tringides and Jörg Schmalian, Iowa State physics professors and Ames Laboratory scientists.

Dat's how Granny whips up a batch o' her 'wonder' brownies...Kitchen Blender Mixes Up 'Wonder' MaterialMay 23, 2014 ~ A relatively new substance called graphene is being hailed as the wonder material of the 21st century, but no one has developed a way to mass produce it.

However, one Irish scientist says he may have a solution. Graphite is another name for pure carbon, a well-known material used for - among other things - pencil lead. But when the layers of graphite are separated into sheets only one atom thick, the material, known as graphene, behaves quite differently. At that level, the atoms form strict geometric patterns, making it not only stronger than steel but also the best conductor of heat and electricity.

Theoretically, graphene could radically change the way we manufacture batteries, computer chips and flexible screens, or approach cancer therapy. Industry experts say separating and manipulating extremely thin sheets of graphene is a huge challenge. One of the things that's been holding this back is a supply of large scale, large quantities of graphene, good quality graphene, at reasonably low cost, said Keith Paton of chemical manufacturer Thomas Swan.

But Jonathan Coleman, at the materials science center of Trinity College in Dublin, says it can be done by mixing graphite with water and a surfactant, a form of soap, in an ordinary kitchen blender. The rapidly rotating blade separates the layers, which stick to the blenders wall. At this early stage there's also graphite in there, so we have to go through a processing stage where we separate the graphite from the graphene and when we do that we get this nice black liquid here and what this is, is graphene in water with surfactant, Coleman said.

Coleman, the project's principal investigator, says once this process is perfected and adjusted for large-scale production, graphene will begin to change the way we manufacture many items - from high-strength plastic to printed electronic circuits. There will be many applications that will involve its conductivity, so if you make a very very thin layer of graphene on a surface that layer is conductive and so, for example, it can be used as electrodes in solar cells or batteries, he said. Scientists say this wonder material could be also used in water treatment plants and for cleaning up oil spills. Large scale production may start by the end of this year.

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